1. Field of the Invention
The present invention relates to a waterproof admixture composition for concrete which is added to fabricate concrete having excellent anti-corrosive performance, and more particularly to a waterproof admixture composition for concrete having excellent anti-corrosive performance which can protect reinforcing steel bars in concrete against oxidation in the presence of salt, thereby exhibiting excellent anti-corrosive performance and thus greatly improving the durability of reinforced concrete. As a result, the waterproof admixture composition for concrete can be effectively used even in salt-damaged areas and corrosive environments and the like.
2. Description of the Related Art
Various structures made of concrete are exposed to special environmental conditions, e.g., physical and chemical conditions, which directly or indirectly affect the concrete structures. Particularly, most concrete facilities are likely to be exposed to moisture such as rain, causing the deterioration in the performance of concrete facilities. As a result, the concrete facilities are considerably reduced in durability.
In order to solve these problems due to moisture, waterproofing treatments are commonly performed on most concrete facilities. However, since the waterproofing treatments are performed by coating a waterproof admixture onto the surface of concrete facilities, concrete facilities which are located in highly humid conditions and coastal areas cannot be sufficiently protected against moisture by the surface coating.
Various kinds of waterproof admixtures capable of preventing the absorption and leakage of moisture in the course of fabricating concrete have been developed and are currently used.
Korean Patent Laid-open No. 89-5242 discloses a powdery waterproof admixture formulated by adding carbon black or an aluminum silicate-based inorganic powder to a fatty acid metal salt and paraffin chloride and mixing the resulting mixture with a polymeric resin and a dispersion agent.
Korean Patent Laid-open No. 87-1288 provides a waterproof admixture composition comprising fly ash as a main component, sodium metasilicate (water glass), zinc stearate as a fatty acid metal salt and a high early strength additive.
Korean Patent Publication No. 87-1543 provides a waterproof admixture comprising fly ash as a main component, methylcellulose, barium chloride, sodium metasilicate, pozzolith and zinc stearate. However, since the barium chloride may cause the corrosion of reinforcing steel bars in concrete due to chlorides generated upon hydrating, the waterproof admixture is unsuitable for concrete structures.
Korean Patent Laid-open No. 01-38952 discloses a spherical powder waterproof admixture composition comprising silica fume as a main component, a higher fatty acid metal salt (zinc stearate), a fluidizing agent, and an AE (air entraining agent) water-reducing agent and silica.
The waterproof admixture powders and compositions mentioned above can increase the water tightness of the concrete using water-repellent components including fatty acid or paraffin as a main component, pozzolan or silica fume, but have problems in that since they deteriorate the strength of concrete facilities, they cause the deterioration in performance and corrode reinforcing steel bars used in the concrete facilities.
Korean Patent No. 356354, which was filled by the present inventors, discloses a spherical waterproof admixture composition for concrete comprising fly ash as an artificial pozzolan activator and silica fume as main components, ethylene vinyl acetate as a redispersible powders polymer, zinc stearate as a higher fatty acid metal salt and naphthalene sulfonate as a high early strength additive. Since the composition exhibits a waterproofing performance comparable to conventional waterproof admixtures, and at the same time, induces improvement in the strength of concrete structures, deterioration in the performance of the structures is inhibited and thus the durability is greatly improved.
Although the waterproof admixture composition attains improved anti-corrosive effects compared to conventional compositions, it has problems that when the composition is utilized on concrete structures located in highly salty coastal and sea areas and environmental contaminant-processing facilities, satisfactory anti-corrosive effects cannot be obtained and thus deterioration in the performance and durability of the concrete structures cannot be avoided.
The concrete structures located in highly salty coastal and sea areas and environmental contaminant-processing facilities contain chloride ions and acidic anions to a considerable extent due to various factors. These ions destroy passivity layers formed around reinforcing steel bars used in the concrete structures, leading to corrosion of the reinforcing steel bars. The corrosion reduces the entire strength of the structures and swells the volume of the reinforcing steel bars to 2.5 times larger than their original volume. Such a swelling pressure forms cracks in the concrete structures. Oxygen and water permeate the concrete structures through the cracks, promoting the corrosion of the reinforcing steel bars and greatly deteriorating the performance of the structures.